1. Field of the Invention
The present invention relates to printing, displaying and other processes involving bit-map images; and more particularly to a system for rotating images prior to printing or displaying on a raster scanning device.
2. Description of Related Art
Data used to create images on raster scanning devices, such as dot matrix printers, laser printers, cathode ray tube displays and other types of digital display systems, is typically stored in a bit-map format. The bit-map is organized so that as data is read from the bit-map, it is presented to the printer or other display as a sequence of data words corresponding to each pixel to be printed or displayed. Typically, the data in the bit-map is organized in an address space so that an automatic address generating system can be used to transfer the data from the storage device to the printer or display. Because of the organization of the data, the orientation of images represented by the data is defined when it is written into the bit-map.
In addition, for some systems, bit-map images are created by combining smaller bit-maps of individual images or characters as a given screen or page of printing is being processed. For instance, individual letters are often addressed from a bank of character bit-maps, called a font memory, that are all oriented to be printed with a normal or vertical orientation on the page.
Occasionally, it is desirable to rotate images which have been stored in bit-maps, such as the bank of character bit-maps mentioned above. By rotating the images, a page can be printed on which the letters appear rotated to the normal or vertical position.
In addition, as data processing systems become more complicated and include different types of printers or other display equipment, it is possible that the orientation of data in bit-maps will be required to be changed depending on the particular printer or display device being used. For example, a first printer may scan the bit-map data in a horizontal line direction while a second printer may have a vertical scan format. In order to adapt the bit-map to a vertical scan format, the organization of the bit-map requires alteration.
While systems for rotating the scan direction of images are known, such systems are impractical or impossible to be used with large bit-map images where substantial amounts of data must be stored and operated upon.
U.S. Pat. No. 4,271,476 issued to Lotspiech, describes one method for rotating the scan format of bit-mapped images. However, the Lotspiech method is relatively slow, requiring steps of reading each data word in its original scan format, transferring only selected bit positions within each word to a temporary storage, and reconstituting the rotated bit-map scan format based on the selected bit positions. Prior art systems for rotating bit map images have been unable satisfactorily to rotate bit-mapped images rapidly and automatically without intensive processing by a controlling computer.